Detection Optical Communication Research Articles

Complete Modeling of Nonlinear Distortion in OFDM-Based Optical Wireless Communication

This paper presents a complete analytical framework for modeling memoryless nonlinear effects in an intensity modulation and direct detection optical wireless communication system based on orthogonal frequency division multiplexing. The theory employs the Bussgang theorem, which is widely accepted as a means to characterize the impact of nonlinear distortions on normally distributed signals. This paper proposes a new method to generalize this approach, and it describes how a closed-form analytical expression for the system bit error rate can be obtained for an arbitrary memoryless distortion. Major distortion effects at the transmitter stage such as quantization and nonlinearity from the light emitting diode are analyzed. Four known orthogonal-frequency-division-multiplexing-based modulation schemes for optical communication are considered in this paper: direct-current-biased optical OFDM, asymmetrically clipped optical OFDM, pulse-amplitude-modulated discrete multitone modulation, and unipolar orthogonal frequency division multiplexing.

Transmission of OFDM-UWB Radio Signals in IM–DD Optical Fiber Communication Systems Employing Optimized Dual Parallel Mach–Zehnder Modulators

A dual parallel Mach–Zehnder modulator (DPMZM) used for electro-optic conversion of multi-band orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radio signals in intensity modulated direct detection optical communication systems is optimized theoretically and through numerical simulation. The optimum DPMZM parameters that allow simultaneous mitigation of the second and third order distortion components created by the joint electro-optic converter and photodiode nonlinearities are identified. The corresponding minimum optical signal-to-noise ratio (OSNR) required to achieve a bit error ratio of 10−9 is also evaluated. An analytical expression showing the relation between the optimum DPMZM parameters under extended voltage levels of the OFDM-UWB signals applied to the DPMZM is proposed and validated. It is shown that the DPMZM performance presents high robustness to deviations from the optimum DPMZM parameters identified. Additionally, it is shown that similar minimum required OSNR levels are obtained with the optimized DPMZM and when the electro-optic conversion is realized by a single MZM.

On the Capacity of Intensity-Modulated Direct-Detection Systems and the Information Rate of ACO-OFDM for Indoor Optical Wireless Applications

In this paper we derive information theoretic results for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) in an intensity modulated direct detection (IM/DD) optical communication system subject to a range of constraints. ACO-OFDM is a form of OFDM designed for IM/DD systems. It is an effective solution to intersymbol interference (ISI) caused by a dispersive channel and also requires less optical power than conventional optical modulation formats. Although the classical Shannon capacity formula cannot be applied directly to an IM/DD system, we show that when ACO-OFDM is used in an IM/DD system, it can be adapted to calculate the information rate of the data-carrying odd frequency subcarriers. As a result conventional water filling techniques can be used for a frequency selective channel. These results are applied to indoor wireless systems using realistic parameters for the transmitter, receiver and channel. The maximum rate at which data can be transmitted depends on the channel, the electrical bandwidth and the transmitted optical power. Even when there is no line of sight (LOS) path, when the electrical bandwidth is limited to 50 MHz and the average optical power is limited to 0.4 W, data rates of approximately 80 Mbit/s can theoretically be achieved.

Metal-insulator-semiconductor photodetectors.

The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III–V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

Polarization and intensity properties of converging J0-correlated Schell-model beams

Based on the cross-spectral density matrix, closed form result for propagation equation of electromagnetic J 0-correlated Schell-model beams (EJSMBs) through a paraxial optical system is obtained and the focusing properties are studied. Both numerical calculation and physical interpretation are obtained. It is found that a tunable dark hollow area, which has potential applications in optical trapping, can be obtained by altering the coherence parameter and the focal length. It is also shown that even though the original field is unpolarized, the beams can become fully polarized in the focal region with its width being tunable by changing the coherence parameter. The relevance of this work to applications such as coherent detection in optical communication is also discussed.

Accurate computations of the nonlinear phase noise and BER in DPSK modulation-balanced direct detection high-speed optical fiber communication systems

This article analyzes the nonlinear phase noise caused by an amplified spontaneous-emission of erbium-doped optical fiber amplifier and self-phase modulation (SPM) in a differential phase-shift keying modulation- balanced direct detection optical fiber communication system. Using numerical methods, the characteristic function of the differential nonlinear phase noise \({\cos (\Delta \varphi)}\) in the received electrical current of signals and the accurate computation formula of the BER are achieved when SPM is dominant comparing to cross phase modulation and four wave mixing. The result is verified by a simulation of a 40-Gbit/s transmission system.

Optical signal detection in the turbulent atmosphere using p-i-n photodiodes

Performance of signal detection for intensity modulated direct detection optical communications systems through the turbulent atmosphere is studied considering statistics of photoelectron count in p-i-n photodiodes. The effect of atmospheric turbulence is modeled as a lognormal process. In this system, the photoelectron count is a conditional Poisson process, where the mean count is lognormal. A normal approximation is derived for this conditional Poisson process, which results in a simple calculation for the probability of miss. The probabilities of miss for quantum-limited detection and detection in the presence of thermal electronic noise are simulated and compared with calculations using the normal approximation. Simulation results match the analytical results. For the thermal noise case, the probability of miss is compared with the probability of false alarm to determine appropriate signal length and detection threshold settings for a required performance. Applying results in this paper, a system designer can determine appropriate signal length and detection threshold settings.

16-level differential phase shift keying (D16PSK) in direct detection optical communication systems

Optical 16-level differential phase shift keying (D16PSK) carrying four bits for every symbol is proposed for direct detection optical communication systems. Transmitter and receiver schematics are presented, and the receiver sensitivity is discussed. We numerically investigate the impact of chromatic dispersion and nonlinear transmission degradations.

Joint Symbol and Frame Synchronization for Direct- Detection Optical Communication Systems

The problem of joint symbol and frame synchronization in direct-detection optical PPM communication systems under the assumption of known slot timing is considered here. The optimum maximum-likelihood (ML) and sub-optimum rules for this joint symbol and frame synchronization problem are derived. The reason of Georghiades's (1985) incorrect ML rule is discussed in this paper.

Importance sampling for analysis of direct detection optical communication systems

Analytical solutions of the performance of optical communication systems are difficult to obtain and often, Monte Carlo simulations are used to achieve realistic estimates of the performance of such systems. However, for high performance systems, this technique requires a large number of simulation trials for the estimates to be in a reasonable interval of confidence, with the number of trials increasing linearly with the performance of the system. We apply an importance sampling technique to estimate the performance of direct detection optical systems, where the gain of importance sampling over Monte Carlo simulations is shown to increase linearly with the system performance. Further, we use this technique to study the performance of optical communication systems employing avalanche photodetectors as well as fibre-optic code division multiple access systems (FO-CDMA). We also show that the quick simulation technique developed can be used for a wide variety of coding schemes, and for the first time, we present a comparative analysis of the performance of FO-CDMA systems employing optical orthogonal codes and prime sequences. In all cases, it is shown that importance sampling simulations require less than 50-100 trials for estimating error probabilities of 10/sup -10/ and below. >

Jitter in the square synchroniser on direct detection optical communications. III. Numerical results concerning white circuit noise

Theoretical assessment of the square synchroniser performance, developed in a previous paper, is used to present and discuss numerical results in the presence of white circuit noise. This fully analytical method permits the optimal design (i.e. minimising timing jitter) of square synchronisers. Taking into account all the relevant parameters, for direct detection optical communication systems, a thorough physical explanation of the presented results and their relevance for practical receiver design is provided. The work is increasingly important nowadays because multigigabit per second transmission rates are being used on direct detection optical systems. It is shown that, for low signal-to-noise ratios and under quite general conditions, the performance of the square synchroniser is better in a signal shot-noise-dominant situation (typical of long-distance communications with APD receivers), followed by the white-circuit-noise-dominant situation (typical of long-distance communications with PIN receivers), and is worst for the dark current-noise-dominant situation (typical of germanium APD receivers). The noise contribution to square synchroniser performance can be very high. The timing jitter properties respecting the circuit noise dominant situation usually hold also on the signal shot-noise dominant situation, except for a very narrow (compared with the bit period) optical pulse shape incident on the photodetector.

An optimum weak optical signal receiver for intensity modulation/direct detection optical communication systems

AbstractThis paper presents a detailed study of a binary optical direct detection optimum receiver for the use of optical space communication systems, where a long‐distance transmission makes optical received signals extremely week. At such a low‐power operation of the receiver, the quantum discreteness structure of the shot noise process is evident in the optical detector output.A statistical model for optical detection output is derived, considering this quantum discreteness, thermal noise at the receiver circuit system, dark current at optical detector, and random photomultiplication. Moreover, the optical detection system is considered as an ideal integration system, and optical detection output is expressed by using a time‐dependent sample value vector.A logarithmic likelihood function derived from this sample value vector on the basis of maximum likelihood testing is studied, and the optimum receiver structure for weak optical signals is clarified. That is, it is shown that, even under the existence of thermal noise and random photomultiplication, primary photon count plays an essential role in signal detection similar to that in the shot noise limited case and the primary photocount estimator‐maximum likelihood detection receiver is derived theoretically. Then the error rate performance is analyzed theoretically and compared with that of a conventional direct detection receiver. As a result, it is shown that by introducing a wide‐band optical detection system, a significant improvement in error rate performance is observed over conventional receivers.

Jitter in the square synchroniser on direct detection optical communications. Part 2: comparison with Franks and Bubrouski's results

For part I see ibid. p. 209. The increasing use of very high bit rate direct detection optical systems with the need for more and more precise clock recovery circuit (CRC) is a justification for the study of CRC performance. In a previous paper, this study was developed for the square synchroniser but its validation needs to be confirmed. In this paper, this confirmation is effected by comparing the results established in that paper with Franks and Bubrouski's work. A relevant outcome of this comparison is that the study of the square synchroniser performance in the direct detection optical receiver can be regarded as a generalisation of the Franks and Bubrouski's study.

Jitter in the square synchroniser on direct detection optical communications. Part 1: theoretical analysis

Very high bit rates (multigigabit per second) are being increasingly used on direct detection optical systems. The influence of clock recovery circuit (CRC) inaccuracies is of special significance in these systems since a small timing error may represent a high fraction of the bit period. Accordingly, it is quite convenient to develop analytical results to compute the jitter arising in the most commonly employed CRC. In this paper, the performance of the square synchroniser in a direct detection optical receiver using the generalised Gaussian approach model for the photodetection and subsequent filtering is evaluated theoretically: a general expression for dynamic timing jitter valid for any type of photodetector (PIN or APD), optical pulse shape, pulse shape at the input to the squarer prefilter, narrow bandpass filter, noise type dominance and signal to noise ratio is presented. A first qualitative analysis of dynamic timing jitter is provided, stressing several differences between these systems and those with additive signal-independent noise.

Prechirp technique as a linear dispersion compensation for ultrahigh-speed long-span intensity modulation directed detection optical communication systems

Prechirp technique, as a linear dispersion compensation for intensity modulation direct detection (IM-DD) optical transmission systems, has been investigated theoretically and experimentally. This technique is based on a predistortion technique in an optical transmitter. Implementation to the ordinary IM-DD optical transmitter, which uses an external intensity modulator, is easily realized merely by adding a small injection current modulation to a semiconductor laser diode, allowable optical transmission fiber dispersion will be more than doubled with this technique, modified prechirp technique, which utilizes a time division superimposing prechirped bit streams, has also been investigated to achieve greater dispersion compensation capability. >

Optimal design for direct-detection system with optical amplifiers and dispersion compensators

System performances of direct detection optical fiber communication systems with optical amplifiers and dispersion compensators are investigated theoretically and confirmed by experimental results for several different configurations. The experimental results agreed well with the calculated results. The theoretical calculation predicts that a 120-km repeaterless transmission of 10 Gb/s is possible through the standard single-mode fiber using only one commercial fiber amplifier and a dispersion compensation fiber at the receiving end. >

Theory of signal degradation in semiconductor laser amplifiers in direct detection systems

Theoretical studies are carried out on long haul direct detection optical fiber communication systems, with inline optical semiconductor amplifier repeaters. Calculations are made of the noise, eye diagrams, and bit-error-rate characteristics of lightwave systems with optical amplifiers. Indications are given of the effect of amplifier characteristics such as spontaneous noise and signal distortion due to gain saturation on the system performance. The nonlinear process within semiconductor laser amplifiers leads generally to pulse amplitude-temporal distortions due to gain saturation. This theoretical study demonstrates that the system penalty caused by these nonlinear effects appears progressively as the optical input power at each amplifier is increased. For example, nonregenerated fiber transmission using traveling wave semiconductor laser amplifiers was simulated, and results obtained at 0.5 and 2.5 Gb/s are presented. In order to improve the system performance, the influence of structure and bulk dimensions of the amplifier cavity is also considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multigigabit subcarrier multiplexed coherent lightwave system

A wideband coherent detection optical communications system using two microwave subcarriers to transmit 8 Gb/s with a RF bandwidth efficiency of 1 b/s/Hz is described. It is demonstrated that two subcarriers each carrying 4 Gb/s QPSK, compactly spaced at just twice the data rate, can achieve a receiver sensitivity ( eta P) of -26.5 dBm with as little as 0.5-dB crosstalk between subcarriers. How the various components affect the overall performance of QPSK-SCM systems, including a CNR model for multichannel systems is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-rate, power-efficient coding for optical communication: Design and performance evaluation

In the direct detection optical communication system which detects the optical pulse by counting the photons, it is known that the information transmitted by each photon has an important role in the performance evaluation of the error-correcting code, in addition to the code rate and the decoding error rate. Especially, for the code which can achieve arbitrarily small error rate by increasing the code length, the performance of the code can be evaluated based on the code rate and the information efficiency. However, these two evaluation measures are in a trade-off relation; and there is a limit if one attempts to improve both. From such a viewpoint, this paper determines the bounds for the code rate and the information efficiency and determines the limit of performance when the ideal error-correcting code is applied to the direct detection optical communication. Then, as a code which can arbitrarily achieve a small error rate, a new code based on the iterated code is proposed. It is shown that if the code rate is less than 0.75, the proposed code can achieve a better information efficiency than the conventional code with the same code rate.

8 Gb/s subcarrier multiplexed coherent lightwave system

The authors describe the first wideband coherent detection optical communications systems using two microwave subcarriers to transmit 8 Gb/s with an RF bandwidth efficiency of 1 b/s/Hz. It is demonstrated that two subcarriers each carrying 4 Gb/s QPSK (quadrature phase shift keying), compactly spaced at just twice the data rate, can achieve a receiver sensitivity ( eta P) of -26.5 dBm with as little as 0.5 dB crosstalk between subcarriers. The results are within 11 dB of the shot noise limit.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>